In the manufacture of certain electronic devices, such as a crystal filter of a type used in signal transmission equipment, components of the device are mounted on a printed circuit board having leads mounted on a pretinned metal header. More specifically, the leads of the printed circuit board extend through apertures in the metal header for mounting the filter on another printed circuit board, and are secured in the header apertures by an electrical insulating material, such as glass, extending about the leads so as to electrically isolate the leads from the header. The metal header also has openings formed therethrough, as for example to permit subsequent access to adjustable parts of the filter after the filter has been enclosed in a pretinned metal cover by soldering a peripheral edge of the cover to a peripheral portion of the metal header. Subsequently, the access openings in the metal header also are sealed in a known manner, to form a hermetically sealed unit.
In soldering the peripheral edge of the filter cover to the metal header, it is essential that none of the printed circuit board leads projecting from the metal header become shorted to the header. Further, it is essential that no solder be permitted to flow through the openings of the metal header into the cover, since this could damage the components of the filter. Accordingly, in the past the soldering of the peripheral edge of the cover to the header has been accomplished by hand, using a soldering iron. This procedure is undesirable because it is inefficient and time-consuming, and usually results in a soldered seam which is of non-uniform construction.
Accordingly, a primary purpose of this invention is to provide a method and apparatus in which a plurality of cover-header assemblies are uniformly soldered simultaneously by passing the assemblies over a solder wave.